1. Field of the Invention
The present invention relates to an electronic recording device, such as a hard disk drive, and in particular relates to reducing or preventing malfunctions of such a device that may arise from electromagnetic noise. The invention is a nationalization of PCT Application No. PCT/GB01/05770, filed on Dec. 24, 2001 claiming priority to Japan Patent Application 2001-000124, filed on Jan. 4, 2001.
2. Description of the Related Art
As is well known, feedback control can be used for head positioning in a rotary recording device, such as a hard disk drive, in which a recording medium is rotationally driven. To be more specific, positional information (servo pattern) recorded on the recording medium in advance is read from a head to identify a current position. A hard disk controller feeds back a deviation between a target address (target position) and the current position to a servo controller, which calculates driving currents to be inputted to a voice coil motor in order to eliminate the deviation. The voice coil motor drives an arm, according to the inputted driving currents, to change the position of the read/write head that is located at the end of the arm. If such a feedback loop functions properly, then the head is moved to the target position (target address). After moving the head to the target track (or a cylinder), reading or writing information via the head is enabled.
If the head receives a disturbance, such as an external impact, before being positioned to follow the target track, a normally functioning servo system detects the disturbance to automatically control the head position. However, if the head follows the target track and receives a disturbance, such as an external impact, immediately after reading or writing is enabled, reading or writing is performed in a state where the head is off the track (off-track state). In the case of a read operation, the head may fail to read and so the read operation may be performed again.
However, things are not simple in the case of writing. To be more specific, information may be written on the disk somewhere other than on the target track on which it was intended to be written. For example, the information may be written in an intermediate region to an adjacent track or written onto the adjacent track in a superimposing manner. Writing to the adjacent track in a superimposing manner is unacceptable since it eliminates original data of the adjacent track. In addition, writing data to the intermediate region makes it difficult to read and potentially leads to reading errors later.
In recent years, information processing terminals having a communication function represented by a portable telephone and a personal digital assistant have become widespread. In these apparatuses, electromagnetic waves are radiated from the apparatuses when in use. Frequencies of the radiated electromagnetic waves are often in the band 800 MHz to 1.5 GHz, or higher frequencies. The frequencies handled in recent years tend to be increasing in accordance with increases in quantity of handled information content and increases in the number of users.
According to experiments and reviews by the present inventors, there are cases where, due to an effect of high frequency and high field electromagnetic waves radiated from these apparatuses, the head positioning on the aforementioned write operation becomes unstable enough to write the information off the desired track. Related to this problem is the trend in recent years towards decreasing track width and the need for high-precision head position control for higher recording density of hard disk drives. Given the increasing storage density and decreasing track widths, the effect of electromagnetic waves on the head position control may cause a greater disturbance during read and write activities.
The electromagnetic waves are believed to induce high frequency signals on a circuit pattern and wiring of a servo control system. These induced high frequency signals adversely effect the servo system. The interaction between high frequency devices and off-track writing errors may lead to a situation where, for example, if a user is operating a personal computer while talking by a portable telephone, information stored in the hard disk drive is unintentionally erased.
It is theoretically possible, by making an electromagnetic wave shield of the hard disk drive perfect, to prevent the above-mentioned unstableness of the head positioning by electromagnetic waves. However, a perfect electromagnetic wave shield is difficult to implement in reality, as well as in terms of the costs involved.
In addition, personal computers and the like often have their cabinets shielded by conductive paint. However, it has been found that, if a ground is not completely established, the shield may actually function instead like a radiation antenna and may emit secondary radiation therefrom, causing the above-mentioned problem.
The write operation errors caused by the electromagnetic waves in the off-track state can also occur in writable rotary recording devices other than a hard disk drive. To be more specific, it also occurs in a writable optical or optical magnetic storage such as CD-R/W, DVD, and MO storage devices, and so on. Moreover, similar things occur in control of robotic arms and other equipment that may require precise movement.
What is needed is a process, apparatus, and system that for inhibiting erroneous control signals due to disruptive electromagnetic signals. Beneficially, such a process, apparatus, and system would specifically prevent erroneous information writing in a recording device under the effect of background electromagnetic waves. The process, system, and apparatus would also adapt to existing equipment with minimal or no modification.